BFG GeForce 7950 GX2 Review: Dual GPU Video Card
Introduction and NVIDIA GeForce 7950 GX2 Technology
Video cards with two GPUs on them are not exactly new. ATI's Rage Fury Maxx was released all the way back in December of 1999 used alternate frame rendering technology, just as we see in use today in SLI and CrossFire configurations. In more modern technology, dual GPU video cards were re-introduced by Gigabyte with the 3D1 series of cards, starting with a dual 6600 GT graphics card they introduced around the time of Computex 2004. Asus followed closely and most recently released a dual-GPU card based on the 7800 GT.
The most intriguing part of these recent developments with the NVIDIA GeForce 6 and 7-series of GPUs is that they were done without an NVIDIA reference design. The engineers at Gigabyte and Asus were solely responsible for the development work in creating these unique 'SLI-on-a-card' solutions. During CES this past January, NVIDIA finally started talking about their dual-GPU video card solution, but in the form of support for Quad-SLI: running two dual-GPU cards in a combined SLI configuration. Even though the technology was demonstrated back in January, nothing has yet been released to the public using these parts until now.
NVIDIA today is announcing the GeForce 7950 GX2 graphics card. The 7950 GX2 is a totally new GPU (well not really) and is a comprehensive dual-GPU solution reference design from NVIDIA. It sports two 7-series graphics cores and 1GB of total memory. It should be quite a beast.
NVIDIA 7950 GX2 Technology
During the initial launch of the 7900 GTX GPU, NVIDIA briefly introduced us to the world of Quad SLI and an NVIDIA-designed dual-GPU graphics card.
This diagram should look fairly familiar to you as it is the basic building block of the Quad SLI platform that has been plastered across the web. On the card diagram you can see the two individual GeForce 7950 GPUs and the two separate banks of 512MB frame buffer. The PCI Express switch in the middle is used to handle communication between the two GPUs and the rest of the system through the main x16 PCIe connection on the motherboard.
The lines between the two 7950 GPUs indicate an internal communication channel used for multi-GPU rendering and on this image that is the only communication the card sees. All of the 7950 GX2 video cards DO have an SLI connection on the PCB, though that is not going to be supported for end users at this time. More on that later.
NVIDIA was adamant that we not refer to this video card as 'SLI-on-a-card.' Why you ask? Well the answer is rather obscure if you ask me: even though NVIDIA had initially marketed the term SLI (in its second iteration) as graphics card feature, they now stress that it is a platform configuration instead. That means they consider 'SLI' to mean an 'SLI-ready motherboard' coupled with two 'SLI-ready video cards.' Sure, the two GPUs on the 7950 GX2 video card are running in the exact same technical configuration that two single-GPU 7900-series cards would on an SLI motherboard, but NVIDIA wants us to call this new card a 'multi-GPU video card.' Okay, whatever, its all semantics to us at this point.
Other news that NVIDIA announced with the 7950 GX2 card is complete support for HDCP on every 7950 GPU that ships. That doesn't necessarily mean that every graphics card vendor is going to include the necessary CryptoROM to complete the HDCP compatibility, but the option is there finally. Maybe now all that talk about HD-DVD and BluRay decoding performance will actually be worth looking at?
This last informational slide from NVIDIA shows us the current status of running two dual-GPU graphics cards in Quad SLI. For end-users in the enthusiast market, the current NVIDIA answer is that they will not support Quad SLI due to driver issues and specific motherboard and BIOS tweaks that are necessary. The release 90 drivers will not be disabling Quad SLI though, so if you are gutsy and have some extra cash, you can still play around with Quad SLI by purchasing two cards beforehand. However, system builders such as Alienware and Dell will be offering Quad SLI systems since NVIDIA can oversee those individual configurations with more precision.
NVIDIA has promised us that Quad SLI will be ready for the enthusiast market soon and will be made available in a future driver release. At least now you have time to start saving!